Table 2. Animal model input parameters used to simulate energy expenditures of two captive Whooping Cranes (one adult male, one adult female) in outdoor and in metabolic-chamber-like conditions.
| Parameter | Value | Source |
|---|---|---|
| Mass (kg) | 5.05 (female) 6.15 (male) | Measured a |
| Fat mass (% body mass) | 10 | Estimate based on values in [40,41] b |
| Body parts with subcutaneous fat | Torso | Assumption that the majority of subcutaneous fat is stored in torso |
| Animal density (kg/m3) | 633.3 | Unpublished lab data from newly dead birds |
| Basal metabolic rate (W) | 11.9 (female) 13.7 (male) | Allometric equation for non-passerine birds: Equation 3 in [42] c |
| Proportion of energy powering physical activity that is released as heat | 0.8 | [43] (General estimate for animals) |
| Core temp (°C) | 40.7 | Measured in [44] for Whooping Cranes |
| Max. core temperature (°C) | 44 | Estimate based on values in [45] d |
| Min. core temperature (°C) | 37.7 | A decrease of 1–3°C in body temperature is characteristic of most birds [46] |
| Solar reflectivity of feathers | 0.62 | Measured e |
| Solar reflectivity of legs and beak | 0.33 | Estimate f |
| Percent of skin acting as free water surface | 0.2 | Based on values used in [47] g |
| Thermal conductivity of flesh | 0.5 | Based on values measured in [48] |
| Maximum O2 extraction efficiency (%) | 31 | [49] (general value for birds) |
| Minimum O2 extraction efficiency (%) h | 2.12 (female) 2.10 (male) | Allometric equation for birds panting: Equation 63 in [50] i |
| Configuration factor for infrared radiation: proportion of animal facing the sky | 0.5 | Estimate |
| Configuration factor for infrared radiation: proportion of animal facing the ground | 0.3 | Estimate |
aAverage of values measured on first and last days of doubly-labeled water measurements.
bFat masses of Whooping Cranes are not available from the literature. The fat mass of the study animals was estimated as follows. A rough minimum boundary on possible fat content was also obtained based on annual October weights of the two study animals, which were available for the female and male for the 6 years and 7 years prior to the study, respectively. If the difference between their weight during the study and their lowest October weights were all fat, they would have at least and 8% (female) and 7% (male) body fat. Other northern-nesting crane species captive at the International Crane Foundation undergo fall weight gains between September and November [41]. However, our measurements were taken in September, when cranes would not have been gaining weight for long if the timing in their weight fluctuation is similar to that of other northern-nesting species. Thus, we assumed the study animals would have a minimal to moderate amount of fat. [40] found that Arctic-nesting Sandhill Cranes averaged 5% (male) and 7% (female) body fat early in spring migration and 23%-24% fat at end of their spring stopover period. 10% represents a moderate body fat percentage between these extremes.
cBody masses shown in this table were used.
d[45] found that body temperature of birds at an air temperture of 45°C was, on average, 3.3°C above body temperature at the lower critical temperature in a review of 28 studies.
eReflectivities of molted Whooping Crane feathers measured using an ASD portable spectroreflectometer (spectral range = 350–2500 nm).
fSee sensitivity analyses in main text.
g Values for the Hawaiian Amakihi (Hemignathus virens) and the Hawaiian Anianiau (Hemignathus parvus) in [47] In this study, modeled water loss values were within ±2SE (standard error) of water loss values measured in metabolic chambers, except for one temperature point.
hMinimum O2 extraction efficiency is used to simulate panting (increase respiratory frequency without increasing the amount of oxygen absorbed into the body) when the modeled animal is under heat stress.
iAllometric Equation (63) in [50] gives fpant/frest where f is respiratory frequency (per second) for panting and normal respiration and M is mass in kg. Normal oxygen extraction efficiency (see value in table) was divided by fpant/frest for each individual.